1,721,090 research outputs found
Causes and Consequences of Novel Host Plant Use in a Phytophagous Insect: Evolution, Physiology and Species Interactions
Get PDFUnderstanding what determines host range--the number and type of different resources used by an individual, population, or species--is a fundamental question in biology. I explore ecological and evolutionary determinants of host plant range in the tobacco hornworm, Manduca sexta. I have taken advantage of both domesticated laboratory populations of M. sexta, and a recent host plant shift in wild M. sexta in the southern US, to examine how the recent evolutionary history, host plant quality, natural enemies and environmental temperatures impact the performance and fitness of M. sexta. Using laboratory experiments, I demonstrated severe reductions in performance and fitness associated with feeding on an evolutionarily novel host plant, devil's claw (Proboscidea louisianica): survival, growth and development rates, immune function, final body size, fecundity and total fitness were all reduced for M. sexta reared on devil's claw compared to their typical host plant, tobacco (Nicotiana tabacum). I found that these costs can be ameliorated under warmer thermal conditions, as the typical negative relationship between body size and rearing temperature was reversed on devil's claw. However, one of the greatest drivers of M. sexta's adoption of devil's claw appears to be escape from an important braconid parasitoid natural enemy, Cotesia congregata. A field experiment demonstrated that the intrinsic costs of using devil's claw were offset by enemy release, resulting in comparable total fitness of M. sexta feeding on devil's claw and tobacco. In general, domesticated laboratory populations of M. sexta exhibited qualitatively similar responses as wild M. sexta; however, there were a few key differences, e.g., domesticated M. sexta exhibited relatively greater reductions in survival and fecundity on devil's claw. My research shows that the selective environment, and abiotic and biotic ecological factors are important components of host range, sometimes interacting in surprising ways to alter overall herbivore fitness and host plant use
Rapid Life History Evolution in an Invasive Butterflies
Get PDFInvasive species are ideal for studying rapid evolution because by definition they are able to successfully adapt to new environments. Species which have been introduced to multiple regions are particularly useful because they are replicated natural experiments; by comparing several invasive populations we can learn if evolution follows a consistent pattern in new habitats, or whether it is context specific. My first two chapters compare the North American and Japanese populations of the cabbage white butterfly (Pieris rapae), a European invasive species. These experiments demonstrate that the butterfly has evolved differences in body size and growth rate in both North America and Japan, but that some traits (development time) evolve in a consistent pattern in response to climate, while others (body size, immune function) are evolve in response to other regional factors. I also tested whether selection on life history traits varied between spring and summer, and whether there was a correlation between body size and development time. I found that while there was stronger selection for rapid development in spring rather than in summer, we also found that development time and body size were largely decoupled, indicating that these traits may be able to evolve in relative independence. In my fourth chapter, I compared how two components of diet (lipids and protein) affected thermal reaction norms in two wild and one domestic population of P. rapae. I found that reducing protein disrupted reaction norms in the domesticated population but not the wild population. These results indicate that reaction norms may be disrupted by protein reduction, particularly in populations that are adapted to high quality diets. In my 5th chapter, I conducted a meta-analysis to develop new ways of measuring phenotypic plasticity and to evaluate whether phenotypic plasticity was related to mean trait value. We measured plasticity in several ways (range or traits produced, slope of the reaction norm, angles of the reaction norm), and found that relationship between trait and plasticity was dependent on the metric used to measure plasticity. These results indicate that some aspects of reaction norms may evolve independently of trait valuesDoctor of Philosoph
Life history evolution in seasonal environments: phenological and environmental determinants of thermal adaptation in Wyeomyia smithii
Get PDFEnvironmental variation poses a major evolutionary challenge to organisms. This is particularly true for seasonal environments where environmental factors fluctuate radically but predictably on an annual basis. Dormant life history stages often evolve to mitigate exposure to harsh seasonal environments (e.g., winter). In addition, norms of reaction, or the relationship between phenotype and environment, often evolve as a response to local environmental heterogeneity. My thesis explores how the seasonal timing of dormancy affects selection on reaction norms of active, non-dormant life history stages in temperate insects. Changing the dates of initiation and termination of winter dormancy changes the thermal habitat experienced during active growth and reproduction. Thus, geographic variation in the timing of dormancy complicates geographic patterns of thermal selection on active life history stages. Using available inter- and intraspecific life history data in conjunction with long-term weather data, I show that geographic clines in dormancy timing cause populations along the cline to experience similar exposure to cold temperatures during active growth. As a result, strong latitudinal trends in the timing of dormancy predict weaker latitudinal trends in thermal adaptation of active stages. I further illustrate this concept by examining geographic variation in the timing of winter dormancy, thermal sensitivity of development, and tolerance to thermal stress in the pitcher plant mosquito, Wyeomyia smithii. The results from W. smithii suggest that selection applied specifically by the thermal environment of the growing season best explains geographic variation in the thermal sensitivity of development time. In contrast, geographic variation in the thermal environment of the entire year best explains geographic trends in thermal stress tolerance of active life history stages. These results suggest two major conclusions. First, thermal sensitivity and thermal tolerance can exhibit local adaptation in populations that also demonstrate local adaptation in diapause timing. Thus the evolution of one type of adaptation does not preclude the other. Second, dormancy timing unquestionably influences direct selection on active life history stages, but correlated selection on overwinter survival may strongly influence temperature tolerance of active life history stages
The long arm of the larva: evolutionary responses to resource availability
Get PDFHow do organisms adapt to environmental heterogeneity? We know that organisms can respond to environmental heterogeneity by expressing phenotypes that are either phenotypically plastic or constant. However, which strategy of phenotypic expression (plasticity versus constancy) will evolve depends on many factors including: the fitness costs of a given strategy, the degree of environmental heterogeneity, and the degree of association among other life history traits that are also evolving to maximize organismal fitness. Food resource availability is an environmental parameter that is frequently heterogeneous. Echinoid echinoderm larvae are one group of organisms, among many, that have been demonstrated to modify the expression of food collection structures depending on food availability. In my dissertation I examined how the aforementioned factors are associated with the evolution of plastic or constant expression of food collection structures using larval echinoids as a model system. I investigated whether plastic genotypes pay a fitness cost for expressing phenotypic plasticity of food collection structures. I reared multiple genotypes (families) of larvae of the sea urchin, Lytechinus variegatus, and examined whether the degree of plasticity of food collection structures is negatively correlated with two fitness measures: total energetic content and larval stomach length (a site of energy storage). I demonstrated genetic variation iii for plasticity among families but did not demonstrate a cost of plasticity, suggesting either that plasticity is inexpensive or that costs of plasticity are difficult to detect. I investigated whether historical changes in the availability of food resources are associated with evolved differences in the constant and/or plastic expression of food collection structures. I examined larval development of seven “geminate species pairs” of sea urchins located in coastal waters on both sides of the Isthmus of Panama. These species have been evolving in the different environments, with respect to planktonic food for larvae, of the eastern Pacific Ocean and western Caribbean Sea for the past approximately 3 million years. I demonstrated that Caribbean species have evolved to grow longer arms relative to body length than Pacific species regardless of food treatment level (a constant response), and also that none of the species have evolved phenotypic plasticity of food collection structures. I investigated whether the evolution of constancy or plasticity of different life history traits are correlated. Specifically, I examined whether evolved and experimentally induced differences in egg size, which represents an endogenous energetic resource for larvae, are associated with the expression of differences in the length and plasticity of length of larval feeding structures. Using two species from the sea urchin genus Strongylocentrotus that differ in egg size, I demonstrated that evolved and experimentally induced differences in egg size are associated with the expression of larval arm length and that evolved differences in egg size are associated with the degree of plasticity of larval arm length
The effects of development and temperature on immunity in Manduca sexta
Get PDFBoth immunity and development are temperature-dependent, but how development and temperature interact to affect immunity has yet to be explored. Here we measure immunity changes during the 4th instar in Manduca sexta larvae under low (18°C), control (25°C), and high (32°C) temperatures. Different immune pathways differed in their responses across development, with the melanization immune response increasing over the course of the instar. Melanization also differed from the control temperature at high, but not low temperatures. There was no significant relationship found between immunity and development or temperature for the encapsulation immune pathway. These results suggest immunity in insects may be weakened as climate change increases the frequency and intensity of extreme heat events as well as average temperatures.Bachelor of Scienc
Extinction risk and diversification are linked in a plant biodiversity hotspot
Get PDFCITATION: Davies, T. J., et al. 2011. Extinction risk and diversification are linked in a plant biodiversity hotspot. PLoS Biology, 9(5): 1-9, doi: 10.1371/journal.pbio.1000620.The original publication is available at http://journals.plos.org/plosbiologyIt is widely recognized that we are entering an extinction event on a scale approaching the mass extinctions seen in the
fossil record. Present-day rates of extinction are estimated to be several orders of magnitude greater than background rates
and are projected to increase further if current trends continue. In vertebrates, species traits, such as body size, fecundity,
and geographic range, are important predictors of vulnerability. Although plants are the basis for life on Earth, our
knowledge of plant extinctions and vulnerabilities is lagging. Here, we disentangle the underlying drivers of extinction risk
in plants, focusing on the Cape of South Africa, a global biodiversity hotspot. By comparing Red List data for the British and
South African floras, we demonstrate that the taxonomic distribution of extinction risk differs significantly between regions,
inconsistent with a simple, trait-based model of extinction. Using a comprehensive phylogenetic tree for the Cape, we
reveal a phylogenetic signal in the distribution of plant extinction risks but show that the most threatened species cluster
within short branches at the tips of the phylogeny—opposite to trends in mammals. From analyzing the distribution of
threatened species across 11 exemplar clades, we suggest that mode of speciation best explains the unusual phylogenetic
structure of extinction risks in plants of the Cape. Our results demonstrate that explanations for elevated extinction risk in
plants of the Cape flora differ dramatically from those recognized for vertebrates. In the Cape, extinction risk is higher for
young and fast-evolving plant lineages and cannot be explained by correlations with simple biological traits. Critically, we
find that the most vulnerable plant species are nonetheless marching towards extinction at a more rapid pace but,
surprisingly, independently from anthropogenic effects. Our results have important implications for conservation priorities
and cast doubts on the utility of current Red List criteria for plants in regions such as the Cape, where speciation has been
rapid, if our aim is to maximize the preservation of the tree-of-life.http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1000620Publisher's versio
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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